Condition control apparatus



I July 8, 1.947.

F. A. BUSSE EI'AL CONDITION CONTROL APPARATUS Filed Au 25, 4944 Patented July 8, 1947 UNITED STATES PATENT OFFICE apolis, Minn., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn.

a corporation of Delaware Application August 25, 1944, Serial No. 551,221

Claims.

The present invention is concerned with a condition control system and more particularly one of the type employing an electronic amplifier for controlling a condition responsive device in accordance with a signal voltage varying with the value of a controlling condition.

The object of the present invention is to provide in'connection with a condition controlling system an arrangement for amplifying without I ment ll having a relatively high temperature A still further object of the present invention is to provide such an arrangement in which a rectifying impedance is connected in parallel with a biasing circuit of a thermionic amplifier, the

conductivity of the rectifying impedance being controlled in accordance with a condition responsive device.

A further object of the present invention is v to provide an arrangement such as set forth in which a signal varying with the value of a controlling condltion is varied in accordance with an impedance element whose impedance varies withthe value of the condition.

A still further object of the present invention is to provide an arrangement in which a signal voltage responsive to the value of the condition is obtained from an impedance bridge and is dependent upon the unbalance of the bridge.

A still further object of the present invention is to provide'an improved type of amplifier having an extremely high gain.

A still iurther object of this invention is to provide a high gain amplifier in which the output circuit of an electronic discharge device is connected in parallel with a portion of a biasing circuit of a further discharge device and is effective upon the first discharge device being,

Other objects of the invention will be apparent from a consideration of, the accompanying specification, claims and drawing of which the single figure is a schematic showing of a condition controlling apparatus-employed in connection with the control of agas burner.

Referring to the drawing for a more detailed understanding of the present invention, the reference numeral I0 is employed to designate our improved condition controlling apparatus. Assoclated with this apparatus is a resistance elecoeflicient of resistance. The apparatus I0 is employed to control in accordance with the resistance value of resistor II the operation of a gas valve 6 controlling theflow of gas through pipe I to a burner 8. The'gas valve 6 may be any type of electrically operated gas valve in which the valve is opened when power is supplied thereto. Such a gas valve may be operated by an electric" rotary motor through a gear train by an electro-magnet. The details of the gas valve form no part of the present invention.

Associated with the main burner 8 is a pilot a burner 9 which is shown as constantly burning. If desired, thepilotburner may be intermittently operated.- In any event, some means would normally be employed to check the flame of the pilot burner before valve 6 is energized. murder to simplify the disclosure, such conventional means is not shown in the present case.

Referring specifically to the condition controlling apparatus ill, the resistance ii is connected so as to form a unit of a resistance bridge i2 comprising in addition to resistor I I, resistors l3, l4, and I5. Resistor II is connected to resistor l5 by conductor l1 and terminal l8. Resistor ii is connected to resistor l3 by conductor I9, terminal 20, and conductor 2!. Terminals 25 and. 26 constitute the input terminals of the resistance bridge, and terminals l8 and 21 the output terminals. The resistor I5 is an adjustable resistor which may be manually adjusted to control the temperature setting of the apparatus. Resistors l3 and H are preferably of material having a negligible temperature coefficient of resistance.

Power for operation of the apparatus is supplied by a transformer 3| comprising a primary The other output termina1 I8 of bridge I2 is connected to cathode 43 by conductors 49 and 58. The condenser 41 is provided for the purposes of increasing the impedance of the grid circuit on the input side of the grid and cathode terminal to match the impedance between thegrid and cathode. A resistor 5| is connected to grid 42 and cathode 43 to serve as a coupling resistor between the bridge I2 and the control grid 42.

A reference numeral 55 is applied to indicate a second electronic discharge device. This device comprises an anode 56, a control grid 51, a cathode 58, and a cathode heater element 59. The discharge device 55 as well as device 48 are both preferably of the vacuum type.

The secondary winding 34 supplies current to the cathode heaters 44 and 59, the upper terminal of secondary 34 being connected to cathode heater 44 by conductor 68,.current limiting resistor 6|, conductors 62 and 63 and conductors 64 and 65. The cathode heater 59 is connected to secondary 34 by a circuit extending from the upper end of secondary 34 through conductor 68, current limiting resistor 6|, conductors 62 and 61, cathode heater 59, and conductors" 68 and 65, back to the other terminal of secondary 34.

The discharge device 55 controls the energization of a relay generally indicated by the reference numera1 12. This relay comprises a relay winding 13 and a switch blade 14 which cooperates with a contact 15. Switch blade 14 is biased out of engagement with contact -15 and is movable into engagement therewith upon energization of relay winding 13. Connected in parallel with relay winding 13 is a by pass condenser 16 which serves to smooth out the current supplied to winding 13 by the discharge device 55. The anode 56 is connected to the lower terminal of secondary 35 through conductors 18, relay winding 13 and conductor 19. The cathode 58 is connected to the intermediate tap 36 of secondary .and resistor 8| to the intermediate tap 36.

Grid 51 is supplied with an alternating out of phase biasing voltage by a connection which extends from the upper terminal of secondary 35 through conductors 82 and 83, resistor 84, condenser 85, conductor 86, and protective resistor 81. It will be noted that this conneotion .=.between grid 51 and the secondary 35 is to the upper terminal of secondary 35 whose phase relationship with respect to the cathode 58 is op. posite to that of the anode connection. The effect of this connection is to accordingly tend during the half cycle in which the anode is positive to render grid 51 sufiiciently negative with respect to the cathode 58 so as to reduce the condenser 88, a resistor 89, and a conductor 98. It will be obvious that any charge existing on condenser 88 will eflect the voltage existing between grid 51 and cathode 58.

The discharge device.48 is so connected into the circuit as to charge condenser 88 under certain conditions of operation. The anode 4| is connected by conductors 92 and 82 to the upper terminal of secondary 35. Cathode 43 is connected by conductors 93 and 94, and 86, and resistor 81 to grid 51. It will be noted that anode 4| and cathode 43 are respectively connected In parallel with resistor 84 and condenser 85. The lower terminal of conductor 93 is connected to ground at 91.

Power is supplied to the condition controlling apparatus from line wires 96 and 81, leading to any suitable source of power (not shown). Line wire 96 is connected by conductor 98, line voltage terminal 99, and conductor I88 to one terminal of primary winding 32. Line wire 91 is connected by conductor I8I, line voltage terminal I82, and conductors I83 and I84 to the other terminal of primary winding 32.

Operation The various elements of the system are shown in the positions which they assume whenthe temperature to which resistor I I is subjected is at or above the desired value. Let it be assumed that resistor II is located within a space which temperature is to be controlled, and which is current flowing through tube 55 to an extent heated by burner 6. Under these conditions, bridge |2 is unbalanced by reason of the ratio of the resistance values of the resistors II and I5 being greater'than the ratio of the resistance of resistors I8 and I 4. Under these circumstances,

terminal I8 is at a potential closer to that of the' with respect to the voltage which is applied to anode 4| through the following circuit: from the upper terminal of secondary 35 through the conductors 82 and 92, anode 4|, cathode 43, conductors 93, 94, and 86, condenser 88, resistor 89, conductor-s 98 and 88, and resistor 8| to the tap 36. When the temperature of the medium to which resistor II is subjected is at the value presumed to exist, namely that slightly above the desired value, the magnitude of the alternating biasing voltage is such that discharge device 48 is essentially nonconductive. Underthese conditions,- tube 55 is like nonconductive due to the biasing connection from the grid 51 through condenser and resistor 84 to the upper terminal of secondary 35. Since tube 55 is nonconductive, relay 12 is de-energized.

Now let it be assumed that the temperature of the medium to which resistor II is exposed, drops to a value below that desired. The effect is to decrease the value of resistor I I and more nearly restore the bridge I2 to balanced condition. This in turn reduces the amount of the alternating biasing voltage that is applied to grid 42, to a point where the discharge device 48 becomes conductive. Thereupon, a, current flow is established graph. Due to the rectifying characteristic of tube 48, this current flow can take place only in- 81 to the lower terminal.

the direction traced. It is to be rated that this current flow is through condenser 88 in such a relay winding I3 over the circuit previously traced.

The energization of relay winding I3 causes switch blade I4 to move into engagement with contact I5 with the result that an energizing circuit is established to gas valve 6 as follows: from line wire 91 through conductor I0l, line voltage terminal I 82, conductor I03, conductor I06, switch blade I4, contact I5, conductor I81, valve terminal I08, conductor I08, valve 6, conductor II8, valve terminal III, conductor H2, line voltage terminal 99, and conductor 98 to line wire 96. The energization of valve 8 as the result of i the establishment of the circuit Just traced causes valve'5 to move to open position permitting gas to flow through pipe I to burner 8, which gas is ignited by the flame from pilot burner 8.

The burner will continue in operation until such time as the operation thereof results in the temperature 'ofthe medium surrounding resistor II. being raised above the desired value. .When this happens, the unbalance of the bridge I2 is again increased to the point where the alternat ing voltage that is impressed between the grid 42 and the cathode 43 is sufficient to render the discharge device 40 nonconductive. When this happens, the condenser 88. is able to discharge through th following circuit: from the lower terminal of condenser 88 through resistor 81, grid 51, cathode 58, conductor 00, and resistor 89 to the upper terminal of condenser 88. The only voltage then existing on grid 5! will be that due to the biasing connection previously traced. Hence, the discharge device 55 will become nonconductive with the result that relay winding I3 will b deenergized. This, in turn, will cause deenergization of gas valve 5, to interrupt the flow of gas to the main burner 8.

The resistor 84 connected in series with condenser 85 is provided-'for the purpose of insuring the correct phase relationship between the biasing voltage impressed upon grid 51 by the connection including resistor 84 and condenser 85 and the voltage impressed upon anode 56. The

resistor 89 functions to providethe' correct t me constant for the charging of condenser 88 so as extremely simple amplifier requiringno rectifier- 6. sistor for resistor 5I. In this embodiment a 5 megohm resistor is employed for resistor 84 and the 0.3 megohm resistor for resistor 89. 'Condenser 85 was a 0.005 microfarad condenser and condenser 88 a 0.2 microfarad condenser. Resistor 81 has a resistance value of 10 megohms. A resistor of 2000 ohms is employed for resistor 8I By pass condenser I6 is a 1 microfarad condenser.

With a circuit having the values given above, we were able to obtain a voltage gain of 32:00 to one. as measured between the output terminals of thebridge and the terminals of relay winding 18. Such a high gain makes possible the maintenance of the desired temperature to a very high degree of accuracy.

Where we have referred to tube as being non-conductive, it is to be understood that this is intended merely .to mean that the tube isnot sufliciently conductive to energize or to supply enough current to relay coil I3 to cause switch blade I4 to be moved into engagement with contact I5. Actually, when the tube 55 is in the condition referred to as nonconductive. an appreciable current may flow through the tube to the relay coil I3. I

- It will be seen that we have provided an improved condition controlling apparatus by which a very small voltage responsive to a condition change is employed to give a desired controllin effect. This is accomplished by the use of an or other means of obtaining direct current power. While we have shown a specific form of our apparatus it is to be understood that this is for purposes of illustration only and that the scope of the inventionis limited solely' by the appended claims.

We claim as our invention:

1. In condition control apparatus; an electrically energized device for controlling the operation of acondition changing means;'an impedance network including an impedance element Viously noted, the resistor 8'! 'is provided for the purpose of limiting the current flowing between the grid and cathode.

While the invention is in no way limited to an arrangement employing elements having any particular values, in one particular embodiment of our invention, we found it particularly desirable to employ MN? and 7F7 tubes for discharge devices 55 and 48. In the same embodiment, re-

sistors I3 and I4 were each 500 ohm resistors, re-

sistor I I a 420 ohm resistor, and resistor I5 a 250 ohm resistor. An 0.02 microfarad condenser was employed for condenser 41 and a 5 megohm revariable in accordance with the value of a condition indicative of the need for operation of said condition changing means; an electronic discharge device having an anode, a cathode, and a control element; a source of power; means including said anode and cathode and said source of power for energizing said electrical device whenever the potential of said control electrode is above a predetermined value; a further impedance connected to said-control electrode for controlling the voltage applied thereto; a bias- .ing connection between said source bf power and said control element; means including a rectifying variable impedance connected in parallel with a portion of said biasing connection independently of said source of power and effective when said impedance has: a suiiiciently low impedance value to impress across said further impedance a voltage such as to raise the potential of said control element above said predetermined value; and means for varyin the impedance value of said rectifying impedance in. accordance with the value of said impedance element.

2. In condition control apparatus; an electrically energized device for controlling the operation of a condition changing means; an impedance network including an impedance element variable in accordance with the value of a condition indicative of the need for operation cf said condition changing means; an electronic discharge device having an anode, a cathode,'and"a control element; a source of power; means ineluding said anode and cathode and said source of power for energizing said electrical device whenever the potential of said control electrode is above a. predetermined value; a condenser connected to said control electrode for controlling the voltage applied thereto; a biasing connection between said source of power and said control element; means including a rectifying variable impedance connected in parallel with a portion of said biasing connection independently or said source of power and effective when said impedance has a sufliciently low impedance value to charge said condenser in such a manner as to raise the potential of said control element above said predetermined value; and means for varying the impedance value of said rectifying impedance in accordance with the value of said M impedance element.

3. In condition control apparatus; an electri cally energized device for controlling the operation of a condition changing means; an impedance network including an impedance element variable in accordance with the value of a condition indicative of the need for operation of said condition changing means; an electronic discharge device having an anode, a cathode, and a control element; a source of power; means including said anode and cathode, and said source of power for energizing said electrical device whenever the potential 01' said control electrode is above a predetermined value; a condenser connected to said control electrode for controlling the voltage applied thereto; a biasing connection between said source of power and said control element; a further electronic discharge device having an anode, a cathode, and a control element; means including the anode and cathode of -said further discharge device connected in parallel with a portion of said biasing connection independently of said source of power and eflecvariable in accordance with the value of a condition indicative of the need for operation of said condition changing means; an electronic discharge device having an anode, a cathode, and a control element; a source of power; means including said anode and cathode and said source 01 power for energizing said electrical device whenever the potential 01' said control electrode isabove a predetermined 'value; a condenser connected to said control electrode for controlling V *voltage applied thereto; a biasing connection between said source of power and said control elecordance with the value of said impedance element. 4

5. In combination; first and second electronic discharge devices each having an anode, a cathode, and a control element; a source of power; connections between the anode and cathode of one of said discharge devices and spaced points 01 said source of power; a biasing connection between said control element and a point on said source of power whose polarity with respect to said cathode is at all times opposite to that of said anode, said connection including a first impedance element; a further impedance element connected between said control element and said cathode; means for applying a signal potential to the control element or said other discharge device; and means connecting the anode and cathode of said other discharge device in parallel with said first impedance element independently of said source oi! power and in series with said further impedance element eflective when the control element potential is such as to render said other discharge device conductive to impress across said further impedance element a voltage such as to render said first named discharge device conductive.

6. In combination; first and second electronic discharge devices each having an anode, a cathode, and a control element; a source of power? connections between the anode and cathode of one of said discharge devices and spaced points of said source of power; a biasing connection between said control element and a point on said source of power whose polarity with respect to said cathode is at all times opposite to that of said anode, said connection including an impedance element; a condenser connected between said control element and said cathode; means for applying a signal potential to the control element of said other discharge device; and means connecting the anode and cathode of said other discharge device in parallel with said impedance element independently of said source or power and in series with said further impedance element and eflective when the control element potential is such as to render said other discharge device conductive to change said condenser so as to render said first named discharge device conductive.

. 7.,In combination; first and second electronic discharge devices each having an anode, a cathode, and a control element; an alternating current source of power; connections between the anode and cathode of one of said discharge devices and spaced points 01' said source oi power; a biasing connection between said control element and a point on said source oi power whose phase relationship with respect to said cathode is opposite to that of said anode; a condenser connected between said control element and said cathode; means for applying a signal potential to the control element of said other discharge device; and means connecting the anodeand cathode of said other discharge device in parallel with a portion 01' said biasing connection and in series with said condenser independently of said source of power and effective when the control element potential is such as to render said other discharge device conductive to charge said condenser so as to render said first named discharge device con-- ductive.

8. In combination first and second electronic; discharge devices each having an anode, a cath ode, and a control element; an alternating current source or power; connections between the anode and cathode of one of said discharge devices and spaced points of said source of power; a biasing connection between said control element and a point on said source of power whose phase relationship with respect to said cathode is opposite to that of said anode, said connection including a first condenser; a second condenser connected between said control element and said cathode; means for applying a signal potential to the control element of said other discharge device; and means connecting the anode and cathode of said other discharge device in parallel with said first condenser and in series with said second condenser and efiective when the control element potential is such as to render said other discharge device conductive to charge said condenser so as to render said first named discharge device conductive.

9. In combination; first and second electronic discharge devices each having an anode, a cathode, and a control element; a transformer includ ing a secondary winding; a connection between the anode of one of said discharge devices-and one terminal of said source of power; a further connection between the cathode of said discharge device and an intermediate tap of said secondary winding; a biasing connection between said control element and the opposite terminal of said source of power, said biasing connection including a first condenser; a second condenser connected between said control element and said cathode; means for applying a signal potential to the-control element of said other discharge device; and means connecting the anode and cathode of said other discharge device inparallel with said first condenser and in series with said second condenser and effective when the control element potential is such as to render said other discharge device conductive to charge said condenser so as to render said first named discharge a device conductive.- I

10. In combination; first and second electronic discharge devices each having an anode, a cathode, and a control element; an alternating m; rent source of power; connections between the anode and cathode of one of said discharge de vices and spaced points of said source of power; a

biasing connection including an impedance between said control element and a point on said source of power whose phase relationship with respect to said cathode is opposite to that of said anode; a condenser and resistor connected in 1 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,003,992 Cockrell June 4, 1935 2,160,037 Shepard, Jr. l May 30, 1939 2,061,011 Vingerhoets Nov. 17, 1936 1,989,829 Specht' Feb. 5,1935 2,144,668 Stoessel Jan. 24, 1939 2,275,368 Krause Mar. 3, 1942 

